Process for the manufacture of formaldehyde by electrosynthesis from carbon monoxideand hydrogen



. gocharcoal.

Patented June 25,1940

PATENT OFFICE PROCESS FOR THE MANUFACTURE OF FOBMALDEHYDE BY ELECTROSYNTHE- SIS FROM OAKBOIW MONOXIDE -AND HYDROGEN Eloi Ricard, Melle, France, assignor to Les Usines de Melle, Melle. France, a corporation of France Application December 24, 1936, Serial'No. 117,614 In France December 24, 1935 4 Claims. (01. 204-31) This invention relates to the manufacture of formaldehyde by electrosynthesis from carbon monoxide and hydrogen. I

' It is known that when a gaseous mixture of 6 carbon monoxide and hydrogen is passed through an electrical discharge field, traces of formaldehyde are formed. It is also known that it has been attempted to obtain greater yields of formaldehyde by lowering the pressure of the gases to 0.5 atmosphere absolute, but that these attempts have given negative results.

I have found that more satisfactory yields ar obtained when the pressure of the gases is reduced to less than 0.15 atmosphere absolute. Seeing that it is at this pressure that anodic glow appears, one is led to believe that it is this anodic' glow itself, and not the electric discharge as has previously been believed, that plays the preponderant part in the electrosynthesis of formal-- 20 dehyde.

' The present invention therefore may be stated as consisting essentially in efiecting the electro-.

synthesis of formaldehyde from carbon monoxide and hydrogen under the influence of anodic glow as or alternatively at a gas pressure of less than 0.15 atmosphere.

. Experiment has shown that, in addition, it is advantageous to choose a charge of between 0.05

and 0.3 milli-amperes per square centimetre of ".0 cross-sectional area of the reaction tube. v

7 Moreover, I have found that the yields obtained under the conditions set forth above may be increased still further if there be arranged, between the two electrodes, i. e., inside the dis- 35 charge field, a solid body which possesses the power of absorbing gaseous formaldehydee. g. active charcoal or silica gel.

The following non-limitative example described with reference to the accompanying diagram- 40 matic drawing will enable the nature of the invention and the manner in which it may be carried out to be well understood:

L Example The discharge apparatus consists essentially of a porcelain column A having a diameter of I about 16 cms. and divided, by means of perforated plates E, into a series of cells F which are alternately devoid of and filled with absorbent Only the cells at the top and. at the bottom have been represented in the drawing.

At the two ends of the column, there are arranged two silver electrodes B and B1 which are spaced at a distance of aboutAO ,oms. from each other and between which there is a diiference of alternating voltage of the order of-20,000

'volts, the discharge current being 20 milliemployed is converted into chemical energy so that the hourly production is increased to 25 gms. of gaseous formaldehyde which are absorbed by the charcoal in the form of polyoxymethylene.

The residual gases which escape through the pipe D and which always consist of an equimolecular mixture of carbon monoxide and hydrogen are again put back into circuit through the pipe C along with the original mixture, so that finally the conversion is complete.

The reacting gases may be derived from any suitable source and in the case of the carbon monoxide it may be produced by starting with carbon dioxide and reducing it to monoxide by using excess of hydrogen.

What I claim is: m

1. The process of preparing formaldehyde which comprises introducing carbon monoxide and hydrogen into an electric glow discharge zone while maintaining a gas pressure of less than 0.15 atm. absolute and thereby effecting a reaction between the carbon monoxide and hydrogen'with the formation of formaldehyde.

-2. A processaccording to claim 1 in which formaldehyde produced is absorbed within the discharge field by means of absorbent material positioned therein.

3. A process accordingto claim 1 wherein the discharge is energized with a current of from 0.05 to 0.3 milliampere per square centimeter of crosssectional area of the reaction space between the electrodes.

4. A process according to claim 1 wherein formaldehyde produced is absorbed inside the discharge field by means of absorbent material positioned therein, said absorbent materialbelng selected from the group consisting of silica gel and charcoal.

ELOI RICARD. 

